The anatomy of a copolymer is presented by N. A. J. M. Sommerdijk et al. in their Communication on page 8859 ff. The amphiphilic double-comb diblock polymer with oligo(ethylene oxide) and peptide chains aggregates to form complex shapes in aqueous solution. From cryo electron tomograms, 3D volumes were reconstructed (shown as a set of slices). Further visualization highlights branches and loops in a folded wormlike micelle (purple) and the channel structure inside a bicontinuous morphology (yellow).

Selective interactions impose a structural hierarchy during self-assembly and are key for rational tailoring of the supramolecular architecture, according to S. L. Tait, and co-workers in their Communication on page 8835 ff. A labile 1D copper-bipyridine coordination system (blue in the STM topographs) is stabilized and ordered through cooperative assembly with terephthalic acid (red) to produce well-ordered self-assembled nanostructures.

Nanocomposites

An inspired design: A new class of nanocomposites can reversibly switch its mechanical stiffness by up to three orders of magnitude in response to its environment. The architecture of the material is inspired by the dermis of the sea cucumber (see pictures), and the mechanically adaptable composites are potentially suitable for use in biomedical applications.

Metastable Compounds

When the energy landscape offers numerous low-energy structures, the synthetic method can determine which structure is formed. In solid-state reactions yielding new crystalline extended structures from solid precursor phases, mass transport coupled with pronounced reorganization of atomic coordination environments is required. The picture shows the reaction of BaO (left) with TiO2 (right) to form BaTiO3 (middle).

Enzyme pairs that catalyze the same reaction but favor opposite enantiomers are known as enantiocomplementary enzymes (see scheme). To create mirror-image active sites, nature can switch the locations of binding sites and/or the locations of key catalytic groups. In this Minireview, X-ray crystal structures of enantiocomplementary enzymes are surveyed and classified into four groups.

Luck or ability? In the field of supramolecular coordination chemistry, impressive advances have been achieved by the augmentation of initial serendipitous discoveries with rational design. Detailed consideration of symmetry and of the basic principles of coordination chemistry have led to rational strategies for the construction of diverse nanostructures with specific form and size (for example, 1; Fe: white, tripodal benzene ligand: yellow).

Blue belt: Condensation polymerization of pyrene (blue) and triphenylene (green) monomers leads to the formation of a hexagonal mesoporous covalent organic framework (see picture). This material exists in a belt shape, absorbs photons over a wide wavelength range to emit them as blue luminescence, and is semiconducting, as well as being capable of repetitive on–off switching.

Trap, kill, and release: An antimicrobial cationic surface can effectively kill bacterial cells and switch to a nonfouling zwitterionic surface which releases dead microorganisms upon hydrolysis (see picture). This biocompatible nonfouling surface can prevent further attachment of proteins and microorganisms and the formation of a biofilm on the surface.

A light switch: A strategy for the photoregulation of hybridization by using the cis–trans photoisomerization of a photochromic nucleoside (PCN) is reported. This process enables the switch between duplexes and single strands in an extremely straightforward and reversible manner with light stimulation (see scheme), even at room temperature. Additionally, installation of PCNs into DNA had little influence on the B-form structure when the duplex was formed.

Ring the changes: A 2D crystalline coordination polymer 1 is transformed reversibly into a 3D crystal 1 a by dehydration. This reversible structural transformation is accompanied by a change in optical and magnetic properties. The 3D coordination framework absorbs H2O molecules but rejects common organic solvents, such as MeOH, EtOH, THF, and Me2CO.

Dysprosium-based single-molecule magnets: Single-molecule magnets (SMMs) of dinuclear dysprosium(III) having thermal and quantum tunneling regimes of magnetization relaxation have been synthesized. Remarkably large energy barriers up to 71 K are observed, in particular for the polymeric complex network, which has the largest energy gap for a lanthanide complex and one of the highest barriers reported for a SMM.

Concise: The first synthesis of the unique azabicyclononane core found in the aeruginosin class of serine protease inhibitors is described. The route is characterized by its efficiency (eight steps) and sets the stage for subsequent introduction of the glycosyl and peptidyl side chains that differentiate the members of the aeruginosin family of natural products.

A luminescent probe for integral membrane proteins (IMPs): Intermolecular sensitization of Tb luminescence is observed in micelles in which the polar head group of a Tb-containing lipid analogue is located close to an antenna chromophore, such as tryptophan, in a surfactant analogue that mimics interfacially bound tryptophan residues of an IMP or tryptophan in the aromatic collar of the vitamin B12 transporter protein BtuB (see picture).

Sequence sets structure: Amphiphilic norbornene-based double-comb diblock polymers with peptide and oligo(ethylene oxide) side chains aggregate in water to form unprecedented complex morphologies depending on the amino acid sequence of the peptide. The internal structures of the aggregates observed by cryo electron tomography show densely folded and highly branched wormlike micelles (left) and spherical aggregates with a bicontinuous architecture (right).

Acting as go-between: A rhodium borate and perborate have been identified as intermediates in the rhodium-mediated oxygenation of pinacolborane (HBpin; see scheme). The rhodium(III)–peroxo complex reacts with the Lewis acidic boron compound HBpin by oxygen transfer from the rhodium center to HBpin to give a rhodium(I) species. The reaction sequence might play a crucial role in the homocoupling of boronic acid.

Two in one: In vitro biotransformations with the cytochrome P450 monooxygenase AurH from the aureothin (1) biosynthetic pathway provided direct experimental evidence that a single monooxygenase can install two CO bonds sequentially to form a tetrahydrofuran ring. Structural elucidation of the intermediate 2 revealed the order of bond formation and the stereochemical course of this unprecedented oxygenation–heterocyclization reaction.

A new class of luminescent dyes incorporates aromatic residues attached by an ethynyl link to the boron center of a subphthalocyanine (SubPc; see picture). Efficient energy transfer from energy-donor subunits to the SubPc produces very large Stokes shifts, while luminescence quantum yields are maintained. An acid-triggered “switching on” of SubPc emission occurs when a dibutylamino fragment is axially coordinated to the SubPc.

La click, c'est chic! A catalytic system based on an [(NHC)2Cu]X complex (NHC=N-heterocyclic carbene) was developed for the [3+2] cycloaddition of azides with alkynes under click conditions (see scheme). This system is broad in scope and highly efficient (turnover frequencies up to 5000 h−1) even at very low catalyst loadings (down to 40 ppm). Preliminary mechanistic studies suggest a specific precatalyst-activation pathway.

Putting the brakes on a hydride shift: The incorporation of a 2-silyloxy group increases both the stability and reactivity of 5-substituted cyclopentadienes, thus facilitating their preparation and use (see scheme; Bz=benzyl, TBS=tert-butyldimethylsilyl). This approach has been applied to the synthesis of the E ring in the marine alkaloid palau'amine.

A sweet library: Two variants (wild-type (WT) and a triple mutant) of glycosyltransferase (GT) OleD have been shown to catalyze glycosylation of over 70 substrates, formation of O-, S- and N-glycosidic bonds, and iterative glycosylation (see scheme). Identified substrates include nucleophiles not previously known to act in GT reactions and span numerous natural product and therapeutic drug classes.

The smaller, the better: In situ synchrotron ambient pressure X-ray photoelectron spectroscopy allows examination of the oxidation state of the surface of the rhodium nanoparticles (NPs) during CO oxidation in an O2 atmosphere. 2 nm NPs oxidize to a larger extent than 7 nm NPs during reaction at 150–200 °C, which correlates with a fivefold increase in turnover frequency for the smaller nanoparticles.

Synthetic Methods

Inexpensive and straightforward: An iron-mediated cross-coupling reaction generates biaryl compounds through CH bond activation, using easily handled reagents with low toxicity. Under the optimized reaction conditions a series of substituted phenylboronic acids were coupled with several simple unactivated arenes.

The many faces of gold: Trisoctahedral gold nanocrystals have been synthesized in a high yield for the first time. Electron diffraction and electron microscopy demonstrate that the nanocrystals are enclosed by 24 high-index facets, such as {221} planes (see SEM image (left) and model (right)).

A large network with a nanonet architecture has been fabricated from tetrakis(p-chlorophenyl)porphyrin by a pressure differential across films deposited on a template. The pinhole migration mechanism of the nanonet assembly is based on controllable dynamic balance.

One step beyond: The first single-step stereospecific transition-metal-catalyzed conversion of allylic electrophiles into monoalkyl diazenes is described. This synthesis of allylic monoalkyl diazenes offers a new strategy for asymmetric synthesis by the reduction of optically active substrates or the use of chiral catalyst systems. Sensitive substrates are reduced in a highly selective manner. Ar=2-NO2C6H4.

Opened and closed: Visible-light photostimulation of 2,3-diuloses I triggers an unprecedented sequential rearrangement: A Norrish type II photoelimination to give an isolable acyclic photoenol intermediate II is followed by an intramolecular enolexo aldolization. The contraction of the pyranose ring in this process leads to a new type of cyclopentitol derivative III. R=acyl, alkyl, silyl group.

Close to perfect enantioselectivity (up to 99 % ee, see scheme) is found for the formation of α-substituted ketones by the asymmetric hydrogenation of enones with an iridium–phosphinooxazoline catalyst. In an operationally simple process, both linear and cyclic substrates react well and afford the desired products in high yields. A wide variety of substituents are tolerated, thus making the method synthetically appealing.

Limited holeliness: Core–satellite nanocomposite catalysts protected by a layer of mesoporous silica have been fabricated through the combination of simple sol–gel and etching processes. As superparamagnetic components are also incorporated, these composite structures are ideal recyclable catalysts. (see plot for performance in repeated cycles of 4-nitrophenol reduction).

The action behind contraction: The metal–organic framework [Cu3(btc)2] displays negative thermal expansion (NTE) over a broad temperature range. This property arises from two coincident mechanisms, each of which are unique for NTE systems: the concerted transverse vibration of triangular organic linkers, and the local dynamic distortion of dinuclear metal centers within the framework lattice.

Gold Hydride Complexes

Golden opportunity: A terminal mononuclear gold(I) hydride complex has been stabilized by an N-heterocyclic carbene ligand (see picture: Au orange, N blue, C gray). The complex is stable to a wider range of conditions than other transition metal hydride compounds and reacts to form a number of different gold(I) species.

Molecular Kinder eggs are generated from N-centered tripodal heptadentate tris(1,3-diketonate) ions (L3−) in the presence of indium ions. The tetrahedral complexes host a cesium ion ([Cs⊂{In4(L)4}]+, see picture) or four protons. Deprotonation of the species [In4(HNL)4]4+ generates the empty cage compound [In4(L)4], which comes with a break of the symmetry in the initial C3-symmetric tripodal ligand.

Structural control by application of ligand-stabilized nanoparticles in heterogeneous catalysis: Highly active and structurally well-defined NiPt nanocrystals can be obtained by colloidal synthesis. When deposited on suitable supports they show immediate activity without any oxidative or thermal pretreatment. The picture shows the development of the catalytic activity of supported colloidal NiPt nanoparticles for the oxidation of CO at 170 °C.

The heat is on! Ferromagnetic materials heated by induction in an electromagnetic field have found synthetic application. Best results were obtained when superparamagnetic nanoparticles coated with SiO2 were incorporated in a microfluidic reactor and transformations were performed under flow conditions. These magnetic particles can be doped with Pd and used as heated heterogeneous catalysts.

Yes, we have blue bananas! Ripening bananas exhibit intense blue luminescence under UV light. Their luminescence arises from fluorescent chlorophyll catabolites which accumulate in the banana peels during ripening; their natural further conversion into nonfluorescent catabolites is specifically inhibited by a previously unrecognized chemical modification.

Nanoreactors

Processes on nanometer-scale dimensions are possible in a mechanically stable, flexible, and monolithic porous 3D carbon nanotube structure (see picture). The nanoscale chemical reactor exhibits an extremely high surface-to-volume ratio of up to 2×107 m2 m3, which depends on the tube diameter and tube separation. This exceeds values for current microreactors by at least two orders of magnitude.

At the micrometer scale: Chemical interactions at the atomic level have been characterized with localized spectroscopy by using magnetic-resonance force microscopy to locate slices of 2.0 μm thickness in a heterogeneous sample (see picture). To recover the chemical-shift information, the field gradient was temporarily switched off by removing its source mechanically. This technique allows high-resolution one- and two-dimensional NMR spectra to be recorded.